I think it only happens with external plugins on the panel, so you could try to create a new panel (which will only contain one unconfigured launcher), move that to the second screen and add new plugins after that. That might work.

Thank you for your response, indeed it seemed to be caused by one of the items in the panel, probably the launcher don't know for sure.
I edited panels.xml in .config to display only the panel above and it works fine now.

Cheers,
Cristian

I think it only happens with external plugins on the panel, so you could try to create a new panel (which will only contain one unconfigured launcher), move that to the second screen and add new plugins after that. That might work.

I'm very interested in more detailed information about what is going on, so if you find something, please let us know.

I have a dual head configuration that crashes xfce4-panel. Before xfce 4.4 I used to have a panel for each monitor by
running it twice. Now, I cannot run it twice and when I try to configure the panel for the second monitor it crashes with
the following error:

** Message: Xfce Menu: screen changed: 1

** Message: No valid plug window.
The program 'xfce4-panel' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadMatch (invalid parameter attributes)'.
  (Details: serial 73639 error_code 8 request_code 56 minor_code 0)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)

Did anyone else get this error?

Cheers,

Cristian